[PATCH v13 12/12] mm: hugetlb: optimize the code with the help of the compiler
From: Muchun Song <hidden>
Date: 2021-01-17 15:17:49
Also in:
linux-fsdevel, linux-mm, lkml
Subsystem:
hugetlb subsystem, memory management, the rest · Maintainers:
Muchun Song, Oscar Salvador, Andrew Morton, Linus Torvalds
We cannot optimize if a "struct page" crosses page boundaries. If it is true, we can optimize the code with the help of a compiler. When free_vmemmap_pages_per_hpage() returns zero, most functions are optimized by the compiler. Signed-off-by: Muchun Song <redacted> --- include/linux/hugetlb.h | 3 ++- mm/hugetlb_vmemmap.c | 7 +++++++ mm/hugetlb_vmemmap.h | 5 +++-- 3 files changed, 12 insertions(+), 3 deletions(-)
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 05fd2db09b78..b685bc4d79d5 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h@@ -792,7 +792,8 @@ extern bool hugetlb_free_vmemmap_enabled; static inline bool is_hugetlb_free_vmemmap_enabled(void) { - return hugetlb_free_vmemmap_enabled; + return hugetlb_free_vmemmap_enabled && + is_power_of_2(sizeof(struct page)); } #else static inline bool is_hugetlb_free_vmemmap_enabled(void)
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index 6b8f7bb2273e..5ea12c7507a6 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c@@ -250,6 +250,13 @@ void __init hugetlb_vmemmap_init(struct hstate *h) BUILD_BUG_ON(NR_USED_SUBPAGE >= RESERVE_VMEMMAP_SIZE / sizeof(struct page)); + /* + * The compiler can help us to optimize this function to null + * when the size of the struct page is not power of 2. + */ + if (!is_power_of_2(sizeof(struct page))) + return; + if (!hugetlb_free_vmemmap_enabled) return;
diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
index 8fd9ae113dbd..e8de41295d4d 100644
--- a/mm/hugetlb_vmemmap.h
+++ b/mm/hugetlb_vmemmap.h@@ -17,11 +17,12 @@ void hugetlb_vmemmap_init(struct hstate *h); /* * How many vmemmap pages associated with a HugeTLB page that can be freed - * to the buddy allocator. + * to the buddy allocator. The checking of the is_power_of_2() aims to let + * the compiler help us optimize the code as much as possible. */ static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h) { - return h->nr_free_vmemmap_pages; + return is_power_of_2(sizeof(struct page)) ? h->nr_free_vmemmap_pages : 0; } #else static inline void alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
--
2.11.0